Currently, automotive fuses are designed to blow under either short-circuit conditions or prolonged overload conditions. Under short-circuit conditions in a circuit protected by a typical, current automotive fuse, an extremely high current can cause a break in a fusible element in a relatively short period of time. This break in the fusible element causes a disruption of the power supply to that circuit, protecting that circuit from the harmful effects of this high current.
Current automotive fuses also open their internal circuitry to cause a disruption in the power supply under prolonged overload current conditions. If, for example, a current of 135 percent of the rated capacity of the fuse flowed through the fuse for thirty (30) minutes or more, the fusible element of the fuse would blow. A drawback of such generally highly reliable fuses is that the breaking of their fusible element cannot be reversed. Once the fuse has blown, it must be discarded and replaced with a new fuse of the same rated capacity.
There are many examples of current circuit breakers, i.e., resettable fuse devices, on the market. These circuit breakers are disclosed in various United States patent, or are known through their apparent sale or distribution in the United States.
Patents disclosing these and other similar devices include U.S. Pat. Nos. 2,133,309, issued to Schmidinger on Oct. 18, 1938; 2,754,391, issued to Prickett on Jul. 10, 1956; 2,846,543, issued to Sivacek on Aug. 5, 1958; 3,004,203, issued to Epstein on Oct. 10, 1961; 3,131,271, issued to Siiberg on Apr. 28, 1964; 3,196,234, issued to Broekhuysen on Jul. 20, 1965; 3,483,360, issued to Perry on Dec. 9, 1969; 3,631,370, issued to Hollis on Dec. 28, 1971; 3,707,694, issued to DuRocher on Dec. 26, 1972; and 3,893,055, issued to Jost et al. on Jul. 1, 1975.
In addition, the Bussmann division of the McGraw-Edison Company, St. Louis, Mo., distributes and sells within the United States a bi-metal fuse. This bi-metal fuse includes a main element which is a composite of two different metals. This main element is normally bowed or flexed in one direction. When the main element is heated, as occurs during current overload conditions, the differences in the expansivity of the two metals causes the main element to snap into a second, bowed position that is opposite to the first, normal bowed position. In this second, bowed position, the circuit breaker opens to interrupt the flow of current through both the breaker and the circuit that the breaker protects. Because this main element is made of two metals, it is believed to be subject to metal fatigue which can result in an increase in inaccuracy and calibration failure. Moreover, the main element flexes constantly while being heated, not suddenly as with the control wire of the present invention.